In conventional overhead valve internal combustion engines, at least two valves reciprocate to provide intermittent communication between intake and exhaust manifolds and a combustion chamber. The valves include valve stems that are disposed in valve stem guides, supporting axial motion in an engine component such as an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the engine head or by gravity flow from an associated rocker arm. Oil flows by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure along a free upper end of the valve stem toward the manifolds and valve heads.
Valve stem seals located between the valve stem and the valve guide serve various purposes. First, they minimize engine oil consumption by metering oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particles that contribute to pollution. Third, they are helpful in minimizing guide wear.
However, increasingly stringent environmental protection regulation requires that vehicle emissions be reduced to produce lower pollution levels. Exhaust particles, as noted above, contribute to this pollution. Emission levels increase by allowing even minuscule amounts of oil past the valve stem seal and down the valve stem and into the combustion chamber. Current valve stem seals, however, are designed only to meter or limit oil flow and are incapable of completely eliminating oil flow down the valve stem and into a combustion chamber.
Accordingly, a valve stem seal is needed that prevents the flow of any oil down a valve stem past the valve guide and into the combustion chamber.